Engines may be configured with direct fuel injectors that inject fuel directly into a combustion cylinder (direct injection), and/or with port fuel injectors that inject fuel into a cylinder port (port fuel injection). Direct injection allows higher fuel efficiency and higher power output to be achieved in addition to better enabling the charge cooling effect of the injected fuel.
Direct injected engines, however, also generate more particulate matter emissions (or soot) due to diffuse flame propagation wherein fuel may not adequately mix with air prior to combustion. Since direct injection, by nature, is a relatively late fuel injection, there may be insufficient time for mixing of the injected fuel with air in the cylinder. Similarly, the injected fuel may encounter less turbulence when flowing through the valves. Consequently, there may be pockets of rich combustion that may generate soot locally, degrading exhaust emissions.
Thus, the above issue may be at least partly addressed by a method of operating an engine including a first port injector injecting a first fuel into an engine cylinder and a second direct injector injecting a second fuel into the engine cylinder. In one embodiment, the method comprises, adjusting a fuel injection to the cylinder between the first port injector and the second direct injector based on the soot load of the engine.
In one example, an engine may be configured with both direct injection and port fuel injection to the engine cylinders. A fuel injection amount, that is an amount of fuel injected into the cylinder, between the direct injector and the port fuel injector may be adjusted based on the amount of particulate matter (PM) produced by the engine (that is, the engine soot load). In one example, the amount of particulate matter produced by the engine may be sensed and estimated by a particulate matter sensor. In another example, the amount of particulate matter produced may be inferred based on engine operating conditions, such as a speed-load condition of the engine, or based on a differential pressure across a particulate matter filter. The fuel injection amount may be further based on the fuel type.
For example, based on engine operating conditions, a fuel injection profile may be determined including an amount of a first fuel injected through the first port injector, and a second amount of a second fuel injected through the second direct injector. In one example, such as at higher engine speeds and loads, the first amount of port injection may be smaller than the second amount of direct injection. The higher amount of direct injection may be used herein to take advantage of the higher fuel efficiency and power output of the more precise direct injection, as well as the charge cooling properties of the injected fuel.
An amount of particulate matter (soot load) generated during engine operation may be estimated by a sensor and/or inferred based on operating conditions. In one example, as the amount of particulate matter generated exceeds a threshold, the fuel injection ratio may be adjusted. For example, as the soot load exceeds a threshold, a fuel injection amount from the direct injector may be decreased while a fuel injection amount from the port injector may be correspondingly increased. Additional spark timing adjustments may be made based on the fuel injection adjustment to compensate for torque disturbances. Further, an alternate engine operating parameter, such as VCT schedule, boost, EGR, etc., may also be adjusted to compensate for the torque transients.
The increase in fuel injection amount from the port injector may be based on the fuel type of the first fuel while the decrease in fuel injection amount from the direct injector may be based on the fuel type of the second fuel. As such, alcohol fuels may generate less particulate matter than gasoline fuels. Thus, in one example, when the alcohol content of the first fuel is higher, the increase in fuel injection amount from the port injector may be smaller. In another example, when the alcohol content of the second fuel is higher, the decrease in fuel injection amount from the direct injector may be smaller.
A rate of change in the fuel injection amounts may be further adjusted based on a rate of rise in exhaust particulate matters levels (or rate of rise in soot load). In one example, in response to a rate of rise in soot load exceeding a threshold (that is, a sudden and rapid rise in soot levels), the increase in fuel injection amount from the port injector and the decrease in fuel injection amount from the direct injector may be increased. For example, the transition from a larger amount of direct injection to a larger amount of port injection may be substantially immediately. In another example, in response to a rate of rise in soot being lower than the threshold (that is, a gradual rise in soot levels), the transition from the higher amount of direct injection to the higher amount of port injection may be performed at a slower rate (for example, gradually). The transition rate may also be adjusted based on the fuel type.
Further still, the fuel injection may be adjusted based on a regeneration operation of a particulate filter configured to store exhaust PMs. For example, a fuel injection amount from the direct injector may be decreased and a fuel injection amount from the port injector may be increased before filter regeneration, when the soot load of the filter is higher. Then, after regeneration, when the soot load of the filter is lower, and the filter is able to store more exhaust PMs, the fuel injection amount from the direct injector may be increased and the fuel injection amount from the port injector may be decreased. Herein, by increasing the amount of direct injection after filter regeneration, the fuel economy benefits of the direct injection may be achieved while the exhaust PMs generated from the direct injection are stored on the filter.
In this way, by shifting, at least temporarily, to a relatively higher amount of port injection as compared to direct injection in response to a rise in particulate matter (PM) levels, exhaust PM emissions may be reduced without substantially affecting engine fuel economy. Further, by optimizing engine injection for a defined limit of PMs, the advantages of both direct injections and port injections may be availed.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.